This invention relates to an article including a composite laminated end portion, for example a tip portion of an airfoil. More particularly it relates to a discrete end or tip barrier bonded at a tip portion of the airfoil, and to a method for making and for repairing a end portion.
Articles such as blading members with airfoils, including fan blades, compressor blades, and various vanes and struts, made of laminated fiber reinforced composite materials, have been used in turbine engines for many years. Various of such composite airfoil structures and methods for making them have been reported in as such U.S. Patents as U.S. Pat. No. 3,883,267xe2x80x94Baudier et al (patented May 13, 1975); U.S. Pat. No. 3,892,612xe2x80x94Carlson et al. (patented Jul. 1, 1975); U.S. Pat. No. 5,375,978xe2x80x94Evans et al. (patented Dec. 27, 1994); and many others.
One important example of a laminated, fiber reinforced composite airfoil is a gas turbine engine composite fan blade reinforced with graphite or glass type fibers in a typical non-metallic resin or polymeric matrix generally described and used in the art. Therefore, the operating temperature capability of such an article can be limited, at least in part, by a Glass Transition Temperature (Tg). As the temperature of the resin matrix approaches the Tg, it becomes less rigid and behave in a xe2x80x9cjelly-likexe2x80x9d state. Such softening behavior of the resin is believed to be the result of activity and increased length of the resin polymeric chain at elevated temperatures.
In such a condition, the resin is more vulnerable to the absorption of liquid such as water, generally in the form of water vapor, at temperatures below the liquid""s boiling point. For example, in a gas turbine engine, this can occur at lower operating temperatures, after engine shut down, etc. As a result of relatively high moisture content in the resin, the Tg can be reduced and the material strength can be reduced to below a design limit. In addition, the typical fiber reinforced structure in the airfoil tip portion, the laminations of which generally are exposed or terminate at an outer surface of the tip portion, can be more vulnerable to delamination that would increase the chance of detrimental moisture absorption. That is particularly significant in the event of a rub between the blade tip and an opposed, cooperating component such as a shroud, or fan case inner surface.
The present invention provides an article with a discrete end barrier bonded with an end portion of an article, for example a laminated composite tip portion of an airfoil, as a barrier to penetration of fluid contacting the end portion, and as applicable as an inhibitor to delamination of a laminated end portion.
In one form, the invention provides an article comprising an airfoil extending between a leading edge and a trailing edge and including a laminated composite airfoil body of a first density, the airfoil terminating at one end in an airfoil end or tip portion. The airfoil tip portion comprises an end or tip barrier discrete from and bonded with the airfoil body. The tip barrier extends substantially between the leading edge and trailing edge and for a distance from a tip portion outer surface toward the airfoil body, and is of a second density substantially no greater than the first density of the airfoil body. The end or tip barrier comprises an end or tip barrier support, substantially impregnable to fluid and including therein passages communicating through the end portion outer surface. Fluid impregnable material is disposed within and closes the passages at least at the end or tip portion outer surface.
In another form, the present invention provides a method for making such an article. In forms of such a method, a laminated composite article, such as a blade, is made to an existing design shape. The portion of the article carrying the end portion, for example the airfoil, is trimmed from its end or tip for a selected distance to provide an article or airfoil body preform. In another form, an article body preform, such as a blade body preform, is made to a selected length that, with an end or tip barrier, will be of an existing design shape. The end or tip barrier support is disposed at the blade body preform and then the fluid impregnable material is disposed in and fills passages of the support. When bonded together, the end or tip barrier is. provided.
In still another form, the present invention provides a method for repairing a damaged end or tip portion of a service operated article, for example an airfoil. In such method, the damaged end or tip portion is removed, for example by machining, grinding, etc. to provide a body preform If a tip cap, for example of metal, has been disposed on lateral surfaces of an airfoil, the damaged tip portion can be removed without removing the tip cap from the airfoil. Then the article is repaired by disposing the end or tip barrier at the body preform, as described above.